The present invention relates generally to traction motors and, in particular, to a process and equipment for locating traction motor armature ground faults.
Typically, it is difficult to locate armature ground faults in large traction motors such as the type used to power electric locomotives. One known method of testing for ground faults involves connecting a 120 volt line source through a resistive light bank to pass current through the armature windings in an attempt to generate smoke at the ground fault location. This method does not always produce observable smoke and, when it works, it only provides an approximate location for the ground fault. When this method does not work, a higher current capacity power source must be used which is destructive to the armature core and also destroyed any evidence of the root cause of the armature defect. Neither the line source/light bank method nor the high current source method is effective in identifying armatures with lower coil ground faults.
A process and an apparatus for locating ground faults in motor armatures according to the present invention includes shorting a commutator of a motor armature with a shorting strap and connecting a variable voltage AC power supply and a load in series between the commutator and a core of the motor armature. The magnitude of a voltage applied by the AC power supply to the commutator is increased until current flows through a winding grounded point on the motor armature. Then a probe of a gauss meter is moved along an edge of the core adjacent the commutator to locate a core slot having a highest magnetic field reading measured by the gauss meter. The probe is moved along the core slot with the highest reading until the gauss meter measures a sudden reduction in the magnetic field indicating the grounded point.
The armature ground fault detection process and equipment according to the present invention utilize an adjustable voltage power supply with a built in current limiting capacity such that only the amount of current required to thoroughly test the armature coils is applied. A magnetic field detecting gauss meter measures the paths of the test current throughout the armature. The meter operator can interpret the measurement results to pinpoint the location of the ground fault thereby enabling repair and analysis of the root cause.
Some of the advantages of using the process and equipment according to the present invention include: eliminating the scrapping or teardown of armatures during production; enabling root cause analysis of armature failures for corrective action to fix failed armatures and to prevent failures in future production; labor savings in reduced testing time; and easy adaptability to AC stators for all types of motors.